Perineum LO1

1. Understand the organization and muscular contents of the pelvic diaphragm.

The pelvic diaphragm/floor is composed of skeletal muscles and associated investing fasciae, and fills the inferior-most aspect of the pelvic cavity. The perineum is inferior/superficial to the pelvic diaphragm. There is an opening in the midline called the urogenital hiatus through which the pelvic viscera pass. The function of the pelvic diaphragm is fairly complex, but it works primarily to resist intra-abdominal pressure and to provide support and stabilize the pelvic viscera. Conceptually, the pelvic diaphragm is a continuous sheet of muscle except for the urogenital hiatus; however, it is divided into different components: levator ani mm. & (ischio)coccygeus mm.

Each levator ani mm. consist of three parts:

    • Puborectalis mm.: Originate on the posterior aspect of the pubic bone, and wrap around (meet counterpart) the rectum to form a sling. Often categorized as a component of pubococcygeus mm.
    • Pubococcygeus mm.: Originate on the posterior aspect of the pubic bone and pubic ramus (lateral to puborectalis mm.), and attach to the coccyx.
    • Iliococcygeus mm.: Originate on the tendinous arch of levator ani (a condensation of the muscular fascia of the obturator internus m.), and attach to the coccyx and anococcygeal raphe. Often appear more aponeurotic than muscular.

The levator ani mm. are supplied by the inferior gluteal a., and innervated by either branches of the pudendal n., or direct sacral nn. (brs. of S3 and/or S4).

(Ischio)coccygeus mm.: Originate on the ischial spines, and insert on the coccyx and inferior portions of the sacrum. Coccygeus mm. lie deep (internal) to the sacrospinous ligaments, and are supplied by the inferior gluteal a., and innervated by direct sacral nn. (brs. of S3 and/or S4).